Precast concrete members are widely used throughout the building industry in large concrete structures such as parking garages, office buildings, stadiums, and warehouses. The precast members are manufactured in a facility and then shipped to the job site and erected to form the desired structure. In general, precast concrete members include floor slab (double tee and others), beam (girder), column, wall panel, etc.
In general, the precast concrete slabs are supported by concrete beams and the precast concrete beams are supported by precast concrete columns or wall panels and those vertical members are supported by the cast in place concrete foundations. All these members may have to be connected together to avoid possible relative movement to one another due to applied loads such as live loads, dead loads, wind load and etc. Connectors are commonly used which are cast into the precast concrete members and field welded together to provide the stability of the structure,
The connectors are subjected to a variety of forces acting on the welded connection formed between opposing connectors. Lateral wind and earthquake loads applied to the building structure may impart horizontal shear forces in the plane of the floor as well as tension forces that have a tendency to pull adjacent structural members apart. Horizontal shear forces may also result from a volume change in the precast members, particularly due to temperature change, as well as shrinkage and creep effects. Vertical shear forces may be imparted on the welded connection in response to loads acting on the load bearing surfaces of the concrete members, temperature variations and other factors as well.
In order to prevent or minimize the relative movement and to increase the strength of the final structure, metal inserts, often called “weldments” are placed at the edges of supporting members and the ends of the members which is being supported. When the members are positioned for final assembly, the metal weldment of one member is aligned with and opposite to a complementary metal weldment in the supporting member (see FIGS. 7 and 8). The complementary metal weldments are welded to each other to join the two weldments. This results in a unitary structure that is much stronger and less prone to movement than'if no means of joining the members were used. While designing the connection and the weldment, the following aspects are considered:
(A) horizontal shear capacity;
(B) tensile capacity;
(C) vertical shear force;
(D) ease of placement or fastening of weldment during production;
(E) ease of placement of the loose welding steel and ease of welding; and
(F) overall material and labor cost.
In the past, the precast member connector has been comprised of one flat steel plate for a field welding surface with multitude rebar welded to the bottom of the plate to resist the horizontal tensile forces along with vertical reinforcing bars or studs welded to the plate for resisting vertical forces. By preparing multiple types of material and welding them together, the material cost as well as the labor cost is very high and adds substantial cost to construction. More importantly, the effect of quality due to human error is very worrisome.
Accordingly, there is a need for a connector which is totally machine made by using a new stamping technique to guarantee the quality and reduce its cost and forms a reliable connection between precast concrete members in the presences of variety of loads.